Durability of concrete is commonly associated with the effects of aggressive environments, such as freeze-thaw cycles, or the penetration of liquids with high chloride ion concentrations into the matrix of the concrete that can degrade the physical and mechanical properties of concrete. Cyclic loading that causes a progressive disruption of the matrix structure by crack initiation and propagation allows aggressive environments to accelerate the rate of deterioration of the concrete and/or the reinforcement. The growth of cracks and their propagation during cyclic loading can be retarded or arrested by fibers incorporated in the concrete and thereby delay the formation of pathways for the penetration of aggressive environments or the formation of corrosion products that disrupt the matrix structure of the concrete. This paper presents test data on the flexural fatigue strength and toughness index of concrete reinforced with three types of metallic and one type of synthetic fiber in volume percentages ranging from 0.1 to 2.0. The beams reinforced with metallic fibers exhibited greater fatigue strength than beams reinforced with synthetic fibers. The fatigue strength increased with fiber volume percentage for each type of fiber. The fatigue strength of the beams varied with the deformed shape of the metallic fibers. The toughness index of the fiber reinforced beams was computed from the area under the static load-deflection curve. The toughness indexes for two of the three types of metallic fiber reinforced beams were greater than for the synthetic fiber reinforced beams. The toughness index increased with fiber volume percentage.

Studies of slag activation by alkalies have been carried out since 1973 at the Institute of Building and Refractory Materials, Academy of Mining and Metallurgy, in Cracow, Poland. Laboratory tests were followed by production of the activated slag on a large scale. It appeared that the new cementing material composed of the granulated blast furnace slag mixed with an alkaline activator showed high strength and corrosion resistance. The present work deals with the problem of reinforcing steel corrosion in the alkali-activated slag mortar exposed to the attack of concentrated chloride solution. The observations of reinforcement in ordinary portland cement (OPC) mortars, OPC plus silica fume (SF) mortar, or OPC plus limestone flour mortar were carried out simultaneously. The resistance of alkali-activated slag mortar to the attack of a solution of high Cl- concentration was proved previously. The effective, protective action of the alkali-activated slag mortar was confirmed by electrochemical measurements and weight loss determination after 365 days' exposure to a chloride solution. A similar effect was found in the case of silica fume or limestone flour addition to the OPC mortar, but the corrosion of the reinforcement was clearly visible, as shown by corrosion pits in the reference standard OPC mortar samples.

Steel barges are often used by British Columbia's forest industry to carry wood chips. Generally, these chips have been offloaded at pulp mills by overhead gantry cranes using grab buckets. In time, this has severely damaged and dented the decks. The industry has recently realized considerable savings by changing the method of offloading so that the chips are placed on conveyors by front-end loaders. In 1989, a barge operator decided to upgrade his existing barge fleet to utilize the new method. This meant that new, smoother decks had to be constructed. The project was tendered with two alternatives: one using a new steel deck and the other a concrete topping. During the tender period, an alternate type of concrete deck was proposed that proved to be substantially cheaper. The method consisted of welding steel studs to the existing deck, placing reinforcement, and pouring a high-strength (55 Mpa) steel fiber reinforced concrete. This is expected to provide improved durability and abrasion resistance.

Compared artificial portland cements (CPA type) without mineral addition and blended portland cements (CPJ) containing 15 to 25 percent filler, while attempting to keep the mechanical strength class of both types constant. The properties studied were: binder hydration, strength variations, types of hydrates, porosity, etc.; effect of seasonal temperature variations; and resistance to various aggressive environmental agents (carbonation, freezing and thawing, seawater, diffusion of chlorides). For constant mechanical strength class, the durability of CPJ cements with fillers is identical to that of CPA without mineral addition.

The measurement of the electrical resistivity of concrete is a nondestructive technique that is rapidly gaining acceptance as a means to evaluate the severity of reinforcement corrosion when used in conjunction with potential mapping methods. The concrete resistivity can be determined in situ from placing four equally spaced surface electrodes in contact with the structure and passing a current between the outer electrodes. A measurement of the voltage between the inner electrodes leads to an assessment of the resistivity of the concrete. One practical difficulty in interpreting resistivity measurements is allowing for the error caused by a surface layer with a resistivity lower or higher than that of the underlying concrete. This could, for example, be due to recent wetting of the concrete or due to carbonation of the surface zone. This effect is discussed, and practical correction curves permitting a true assessment of the resistivity of the underlying concrete are given. A very dramatic error in resistivity measurement can occur when there are two surface layers with resistivities--one lower and one higher--than the underlying concrete, such as might be caused by a recent wetting of concrete already having surface carbonation. This wetting can cause a paradoxical increase in the apparent resistivity of the concrete in excess of one order of magnitude. The results of experimental and theoretical studies are presented. The reasons for this effect are discussed, and practical guidance for in situ resistivity measurement is given.